The present invention relates to a cooling pipe structure for an arc furnace used for steel making or the like.
In recent years, arc furnaces for steel making are used in increasingly hard conditions, since they have become larger and are operated at higher voltages and higher currents because of the larger capacity transformers adopted for such larger-sized furnaces. Therefore, the life of the refractory linings used for the furnace bodies have become very short.
In this situation, instead of refractories such as bricks, various types of metallic water-cooled furnace structures such as jacket or box type structure U.S. Pat. No. 4,207,060, steel pipes enclosed in casting, piping panel, etc. have been contrived. To overcome the disadvantage of jacket or box structure, viz. the disadvantage that the metallic plates in portions exposed to the high heat in the furnace are liable to be deformed and/or cracked by the thermal fatigue and thermal deterioration caused by repeated expansion and contraction, several different cooling water pipe structures have been contrived and used; one prior art structure shown in U.S. Pat. Nos. 3,843,106 and 4,021,603 has the cooling water pipes enclosed in casting, a second prior art structure shown in U.S. Pat. No. 3,829,595 has the cooling water enclosed in casting embedded in bricks at predetermined intervals, and a third prior art structure shown in U.S. Pat. No. 4,207,060 has the cooling water pipes formed into serpentine coil to define a cooled panel.
The structure shown in U.S. Pat. Nos. 3,843,106 and 4,021,603 is excellent in mechanical strength and spark resistance through scraps with respect to graphite electrodes. Upon generation of spark, merely the surrounding casting is partially melted, blown off and scraped off, and the pipes through which water flows are not affected by the spark, so that no water leakage occurs. However, this structure is disadvantageously heavy and expensive. The structure of U.S. Pat. No. 3,829,595 is very low in the effect of cooling the surrounding bricks by cooling water pipes embedded into the cast steel, and involves the difficulty of brick laying. Therefore, it is little adopted now. The structure of U.S. Pat. No. 4,207,060 has the cooling water pipes bent or has U-shaped pipes welded, to be zigzag, neighboring sections of pipes being arranged in a contacting relation, each of the pipe sections being connected along its length to the neighboring pipe sections of cooling pipe by a welded joint. In summary, each pipe of this panel is free of thermal deformation, free of thermal expansion and free supporting. Therefore, weld joints such as U-shaped caps exist in portions exposed to the high heat in the furnace, and cracks threaten to be caused by the thermal fatigue and thermal deterioration caused by repeated thermal expansion and contraction.
In addition, the different structures of the prior art of the cooling water pipe panels have almost a flat and therefore, they do not allow a thick splash film of slag, etc. to adhere and be held. As a result, it makes the large heat loss of the furnace.
The object of the present invention is to overcome the above mentioned disadvantages of these water cooled furnace structures, providing cooling structures which are safe, low in heat loss and long in life.
Examples of the present invention are described below with reference to the drawings.